A Biofuel Cell with Electrochemically Switchable and Tunable Power Output

Abstract

An electroswitchable and tunable biofuel cell based on the biocatalyzed oxidation of glucose is described. The anode consists of a Cu(2+)-poly(acrylic acid) film on which the redox-relay pyrroloquinoline quinone (PQQ) and the flavin adenine dinucleotide (FAD) cofactor are covalently linked. Apo-glucose oxidase is reconstituted on the FAD sites to yield the glucose oxidase (GOx)-functionalized electrode. The cathode consists of a Cu(2+)-poly(acrylic acid) film that provides the functional interface for the covalent linkage of cytochrome c (Cyt c) that is further linked to cytochrome oxidase (COx). Electrochemical reduction of the Cu(2+)-poly(acrylic acid) films (applied potential -0.5 V vs SCE) associated with the anode and cathode yields the conductive Cu(0)-poly(acrylic acid) matrixes that electrically contact the GOx-electrode and the COx/Cyt c-electrode, respectively. The short-circuit current and open-circuit voltage of the biofuel cell correspond to 105 microA (current density ca. 550 microA cm(-2)) and 120 mV, respectively, and the maximum extracted power from the cell is 4.3 microW at an external loading resistance of 1 kOmega. The electrochemical oxidation of the polymer films associated with the electrodes (applied potential 0.5 V) yields the nonconductive Cu(2+)-poly(acrylic acid) films that completely block the biofuel cell operation. By the cyclic electrochemical reduction and oxidation of the polymer films associated with the anode and cathode between the Cu(0)-poly(acrylic acid) and Cu(2+)-poly(acrylic acid) states, the biofuel cell performance is reversibly switched between "ON" and "OFF" states, respectively. The electrochemical reduction of the Cu(2+)-polymer film to the Cu(0)-polymer film is a slow process (ca. 1000 s) because the formation and aggregation of the Cu(0)-clusters requires the migration of Cu(2+) ions in the polymer film and their reduction at conductive sites. The slow reduction of the Cu(2+)-polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell. The electron-transfer resistances of the cathodic and anodic processes were characterized by impedance spectroscopy. Also, the overall resistances of the biofuel cell generated by the time-dependent electrochemical reduction process were followed by impedance spectroscopy and correlated with the internal resistances of the cell upon its operation.

Polyelectrolyte Complex Membranes for Immobilizing Biomolecules, and Their Applications to Bio-analysis

“…85 Polyelectrolyte complexes have been found to be suitable for use as a matrix in the assembly of mediator-type EFCs. In fact, mediator-type EFCs, which use a mediator, such as vitamin K3, 86,87 Cu 2+ ion, 88 or ferricyanide ion, 86 have been developed.…”

Analytical Techniques for Characterizing Enzymatic Biofuel Cells

“…Common solutionbased mediators are hydroquinone, 16 many types of organic dyes, [24][25][26] ferricyanide, 27 and transition metal complexes. [28][29][30][31] The most efficient electrocatalysts are redox species that have high catalytic reaction rates and low overpotentials.…”

“…Electrochemical impedance spectroscopy is also commonly employed for analysis of enzymatic electrode systems 16 by overlaying a range of AC perturbation signals to an electrode that is under DC bias. A Nyquist plot (a plot of the imaginary part of the impedance versus the real part of the impedance for different frequencies) is generated, and variations of the frequency response can then be used to interpret limiting mechanisms associated with charge transfer.…”

Enzymatic Biofuel Cells—Fabrication of Enzyme Electrodes

“…The maximum extracted power from the cell is 4.3 µW at an external loading resistance of 1 kΩ. The slow reduction of the Cu 2+ polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell [94].…”